The extreme architecture deviating from 1-dimensional chain would be a 3-dimensional cluster. We recently study 3D clusters of molecular nanoparticles in bulk state. Such cluster, a giant molecule, is a new class of soft matter having 3D shapes and composed of chemically linked rigid molecular nanoparticles.Unlike polymer chains that can always reptate regardless of chain length, there exists an upper critical diameter ~ 5 nm for giant molecules. Above it, giant molecules in bulk would be immobile, reaching a cooperative glass-like state. Below it, they show Zimm-like dynamics. The analysis shows that this critical diameter for the structural cluster is also the critical length scale for the dynamical cluster (the cooperative rearranging region).It is thus anticipated that shape-persistent giant molecules not only demonstrate diverse dynamics as a new class of soft matter but also can serve as a new bridge between polymers and colloids, and a new platform to mimic cooperative rearrangements and dynamic heterogeneities.